In a bifocal plastic lens, generally, a bench lens and a small lens are constituted by the same resin. When the small lens is designed to have a smaller radius of curvature than the radius of curvature of the bench lens and a diameter of the small lens is increased in order to widen a near-sight view, an area of a far-sight section of the lens becomes small so that a field of far-sight view is reduced. When an upper part of the small lens is removed, a step is generated therein. Since the step is processed to be a plane, a boundary can be seen clearly. A mold for molding the step is hard to handle because a step portion is easily broken, and is hard to release in a molding process. Thus, there are many problems in respect of the processing. JP-A-49-88534 has described the prior art in which a step is not provided on an upper edge part of a small lens portion but the small lens portion is buried in a lens. In the invention, in order to bury a small lens formed of glass into a lens, a small lens formed of glass is disposed in a shell for casting and molding a plastic lens by using a support member and a resin monomer for a lens is then cast into the shell and is thus heated and polymerized, and a small lens is fixed into the lens. However, the support member remains in the lens. For this reason, a lower part of the cast lens is cut away for use. In addition, JP-A-53-124570 and JP-T-9-511191 have described a method of superposing and combining two types of lens-shaped resin members, thereby manufacturing a bifocal lens, in which a small lens portion takes a protruded shape.